جستجوی مقالات مرتبط با کلیدواژه « Source » در نشریات گروه « فنی و مهندسی »

This paper introduces a versatile single-phase seven-level inverter for integrating lower voltage renewable energy sources to the higher voltage amplitude power grids. The input voltage was increased by combining the voltage of the capacitors in the predetermined current paths. The output staircase waveform was formed by using a DC voltage source, two capacitors, and the aid of the phase disposition pulse width modulation (PD-PWM) strategy. The self-voltage balancing ability of the capacitors without the need for any external controllers nor sensors, high efficiency, and ease of operation were the most important features of the proposed converter. Requiring fewer semiconductor devices compared to other inverters mentioned in recently published papers ensures the superiority of the proposed boosting multilevel inverter. The ability to increase the input voltage by three times at the output in addition to the ability to self-balance the voltage of the capacitors without the use of a side control circuit or sensor were other advantages of the proposed structure. Furthermore, by calculating the power losses and circuit capacitances, 95.8% efficiency was obtained. Finally, the performance of the proposed seven-level inverter under different load conditions was simulated in MATLAB SIMULINK environment and the results were confirmed by the results obtained from the laboratory prototype.

According to the comparison of desalination systems and other energy consuming processes, it is observed that the energy consumption rate of desalination systems is high than that of others. Solar energy is one of the best forms of renewable energies in the world. Therefore, recently, the utilization of solar energy for setting up desalination systems has become quite widespread. Common exergy analysis method by ``Stream wise'' uses input and output exergy of streams assess the exergy efficiency and irreversibility. In the present study, an exergy analysis method namely ``Sink and Source'' is illustrated. The common exergy analysis method usually computes a system's efficiency by more than a rational value. For example, computed exergy efficiency of a high- capacity system through the Stream wise method is 91.84%, while exergy efficiency of a high-capacity system is assessed to be 7.43% through the Sink and Source method. The inefficiency of the traditional method is also shown in the analysis of a low-capacity system. For example, the computed exergy efficiency of a low- capacity desalination system through the Stream wise method is 96.77%, while exergy efficiency of a low- capacity desalination system is 19.57% through the Sink and Source method. There is a theory about the reverse relation of utility fluid temperature and exergy efficiency of systems. The validation of the mentioned theory is measured by Sink and Source exergy analysis method. In the following, in order to reduce energy consumption of the analyzed system, a solar field is suggested for a high- capacity system. Due impossibility of implementing of the mentioned solar field in Iran and the low efficiency of high-capacity desalination plants, a new low-capacity desalination plant is suggested by the imposition of little changes on operating parameters of the high-capacity system. The presented low- capacity desalination system has higher exergetic efficiency and is capable of working with non-concentrating solar collectors. Finally, the proposed argument is validated based on the obtained results, and it is shown that the Stream wise method loses its functionality in some conditions.

Nitrate contamination of groundwater has been concerned as one of the major environmental problems during last few decades. Recent studies have established that the nitrogen (N) and oxygen (O) isotopes of nitrate (NO3) can be used to trace nitrogen dynamics including identifying nitrate sources and nitrogen transformation processes. Stable isotope ratios (δ15N–NO3, δ18O–NO3 and δD-H2O) of groundwater samples were determined used to identify contamination sources and transformation processes occurring in Varamin aquifer, Southeast Tehran, Iran with intense human activities. The approach is based on the realization that NO3 originating from different sources would be exhibit differing isotopic compositions. In addition, δ18O–NO3 is more useful to identify nitrate from atmospheric sources and nitrogen transformation processes. In case study, nitrate concentration of groundwater were in the range of 0.4 to 79.59 mg/l with mean value of 25.14 mg/l. The nitrogen and oxygen isotopic compositions of nitrate in pore water extracts from groundwater samples indicate at least two potential sources of nitrate in Varamin Aquifer. These sources include animal and human waste as well as soil N that most common sources of nitrate contamination in groundwater are wastewater. Denitrification process occurred in the West and South West of Varamin aquifer, specially.

Acoustic wave propagates properly in water، whilst most forms of electromagnetic waves، particularly in salty and dense sea water، are attenuated after a few tens or hundreds of meters so that it will be impossible to trace and detect them. This paper presents a special method for recognizing probable underwater currents، and reconstruction of their intensities، widths، and directions by using the acoustic waves. The method relies on the differences in travel times of sound in the locations where the water density varies from one place to another. The design is based on the «rotating sound source-receiver» system. This technique is somehow similar to the customary methods of image reconstruction in diagnostic tomography. A computer program was written in Visual C in the Windows media. The efficiency and accuracy of the program was consequently evaluated by simulating an ocean tomographic region and its postulated currents.

Nitrate in high dosage may cause serious diseases for both human beings and animals. WHO has set 45 mg/l as the maximum permitted level for nitrate in drinking water. High concentrations of nitrate in drinking water of the Mian Jungle region of Fasa, located 120 km south east of Shiraz, caused inhabitants to avoid using groundwater as the source of drinking water. Main objectives of this study were i) to determine the main sources of nitrate in the groundwater and ii) to introduce a feasible nitrate removal method in the region. Monthly groundwater sampling were carried out from April 2010 to March 2011 for 15 sources including water wells and outcropped springs. Nitrate, EC, and pH were measured in situ, however remaining parameters were determined in the lab using standard methods. Amounts of nitrate changed from 3.1 mg/l to 259.4 mg/l in diferent times and locations in this region. Results showed that an internal and external background of nitrate in groundwater are originating from the geologic formations and the animal husbandry activities as the main sources.